The mean lifetime of a tire is 37 months with a standard deviation of 8 months. If 127 tires are sampled, what is the probability that the mean of the sample would be less than 38.85 months? Round your answer to four decimal places.
Solution :
Given that ,
mean = = 37
standard deviation = = 8
n = 127
= 37
= / n = 8/ 127=0.71
P( <38.85 ) = P[( - ) / < (38.85-37) / 0.71]
= P(z <2.61 )
Using z table
=0.9955
probability= 0.9955
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